The HVAC systems generally incorporate molded plastic casing sections that are joined together by various means. If the joint between the sections of the casing does not have an air tight seal then it is possible for air to leak from the casing, which results in a loss of comfort in the passenger compartment, a whistle type noise, or both. The noise can cause a reject by the vehicle assembly plants and increased warranty costs.
There are several methods to provide sealing at the joints of the casing. One method is to use a tongue and groove joint. To maintain moldability of the casing section and assemble-ability, the tolerances are such that only at maximum material condition does the tongue have line on line contact in the groove. At all other conditions, there is a gap between the tongue along the flat surfaces surrounding the tongue, i.e., the surface from which the tongue extends. The warping of the casing and possible spreading of the casing can open up this gap at the joint thereby allowing air to flow around the tongue and through the outer gap and creating a leak and/or whistle. Other methods relate to putting a sealing material, such as foam or sealant, between the two sections of the casing to seal any irregularities. These additional seals add cost and can be miss-assembled. It is desirable to provide positive sealing without using separate or additional foam pieces that can increase production time and increase costs.